The people of Narnia adored their giving, caring, Magnificent High King. To them, he was the man that played with the children of the palace, grasped the hands of grieving widows, and ensured that all citizens of Narnia could live in peace. To ensure that peace, however, Peter had to become something entirely different to the enemies of Narnia.
To his enemies, he was the ferocious Sir Peter Wolfsbane who went mad within the heat of battle. Who mercilessly slayed his enemies. Who would obliterate anything or anyone that crossed his path when he was enraged.
High King Peter the Magnificent and Sir Peter Wolfsbane were entirely different people, and for this the citizens of Narnia thanked Aslan himself.